1. Field of the Invention
The present invention relates to a boiler (multi-tube once-through boiler).
2. Description of the Related Art
A boiler has conventionally been well known which is equipped with a boiler body having a water tube group arranged in an annular fashion. In such a boiler, a burner is generally arranged at the center of the water tube group. That is, in a boiler of this construction, the portion at the center of the water tube group arranged in an annular fashion functions as a combustion chamber for burning the fuel supplied from the burner.
Further, regarding conventional boilers, in order to increase the amount of heat recovered from the combustion gas produced by the burner, a technique is known according to which predetermined water tubes constituting a water tube group are equipped with fins (see, for example, JP 02-75805 A).
However, the above conventional boiler has a problem in that effective heat recovery can not be conducted depending upon the positions of the fins installed on the water tubes. That is, the expansion heating surfaces provided on the water tube group constituting the boiler are not effectively utilized. Further, in some cases, the fins overheated by the combustion gas are cracked or detached.